This invention relates generally to gas turbine engines and, more particularly, to clearance control of the turbine section thereof.
Turbine efficiency is directly related to the maintenance of a minimum clearance between the rotating turbine and its associated stationary shroud. Execessive clearances between the components represent a direct performance loss, and interference between the components results in wear to one or both and subsequent excessive clearance operation at other performance levels. Ideally, both the turbine structure and its surrounding shroud are round in shape with minimal clearance between the two components. However, if either the turbine or the shroud becomes "out of round", an excessive clearance gap, or an interference or both, will occur. Such an out-of-round condition may occur from either mechanical or thermal nonuniformities in the circumference of the shroud or its supporting structure. It is therefore essential to maintain substantially uniform temperatures around the circumference of such supporting structures.
The transition cavities between rotating turbine stages and their stationary vanes are subject to hot gas recirculation which represents a loss of available, useful energy and exposes the stationary parts to nonuniform circumferential temperatures which, in turn, cause them to become out of round. In addition to the resulting loss of optimum clearances, discoloration, erosion and cracking of the stationary elements results in these regions of stagnation.
It is therefore an object of the present invention to maintain a minimum clearance throughout the circumference of a turbine blade/shroud combination.
Another object of the present invention is the provision for a turbine shroud structure which maintains a substantially round profile over a range of operating conditions.
Yet another object of the present invention is the provision in a turbomachine for the elimination of hot gas recirculation in the vicinity of the turbine shroud/vane transition area.
Still another object of the present invention is the provision in a turbomachine for preventing the flow of the hot gas stream between the interconnection of the turbine shroud and associated downstream vane.
Another object of the present invention is the provision for preventing the hot gas leaving the rotating stage from stagnating against the leading edge of the downstream nozzles.
Still another object of the present invention is the provision in a turbomachine for a turbine shroud/vane interconnection which is economical to fabricate and effective in use.
These objects and other features and advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.